Structure evaluation system, structure evaluation apparatus, and structure evaluation method

ABSTRACT

According to an embodiment, a structure evaluation system includes a plurality of sensors, a position locator, a velocity calculator, and an evaluator. The sensors detect an elastic wave generated from a structure. The position locator derives a wave source distribution of the elastic waves generated from the structure, on the basis of the elastic waves. The velocity calculator derives a propagation velocity of the elastic wave generated from the structure, on the basis of the elastic waves. The evaluator evaluates the soundness of the structure on the basis of the wave source distribution and the propagation velocity of the elastic waves.

TECHNICAL FIELD

The present invention relates to a structure evaluation system, astructure evaluation apparatus, and a structure evaluation method.

BACKGROUND ART

In recent years, problems related to aging of structures such as bridgesconstructed during the period of high economic growth have becomenoticeable. Because loss is immeasurable when an accident occurs in astructure, technologies for monitoring a state of a structure have beenproposed. For example, a technology for detecting damage to a structureby an acoustic emission (AE) method in which an elastic wave generateddue to occurrence of an internal crack or development of an internalcrack is detected by a high-sensitivity sensor has been proposed. AE isan elastic wave generated due to development of fatigue crack of amaterial. In the AE method, an elastic wave is detected as an AE signal(voltage signal) by an AE sensor using a piezoelectric element. The AEsignal is detected as an indication before breakage of the materialoccurs. Therefore, the frequency of occurrence of AE signals and thesignal intensity are useful as an index indicating the soundness of thematerial. For this reason, studies are being carried out on technologiesfor detecting signs of deterioration of structures by the AE method.

When a load due to traffic or the like is applied on a concrete floorslab of a bridge, AE occurs due to crack propagation, friction, or thelike in the floor slab. By installing an AE sensor on a surface of thefloor slab, the AE generated from the floor slab can be detected.Moreover, by installing a plurality of AE sensors, a position of an AEsource can be located from a difference in arrival time of AE signalsbetween the AE sensors. A degree of damage to a target floor slab isestimated from the result of locating the position of the AE source.However, when the correspondence between the location result and thedegree of damage is not sufficient, stable soundness evaluation cannotbe performed in some cases. Such a problem is not limited to concretefloor slabs of a bridge but is a problem common to all structures inwhich elastic waves are generated as cracks occur or develop.

CITATION LIST Patent Literature

[Patent Literature 1]

Japanese Unexamined Patent Application, First Publication No.2004-125721

SUMMARY OF INVENTION Technical Problem

An objective of the present invention is to provide a structureevaluation system, a structure evaluation apparatus, and a structureevaluation method capable of evaluating soundness of a structure inwhich elastic waves are generated.

Solution to Problem

According to an embodiment, a structure evaluation system includes aplurality of sensors, a position locator, a velocity calculation unit,and an evaluator. The sensors detect an elastic wave generated from astructure. The position locator derives a wave source distribution ofthe elastic waves generated from the structure, on the basis of theelastic waves. The velocity calculation unit derives a propagationvelocity of the elastic wave generated from the structure, on the basisof the elastic waves. The evaluator evaluates the soundness of thestructure on the basis of the wave source distribution and thepropagation velocity of the elastic waves.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a system constitution of a structureevaluation system 100 according to an embodiment.

FIG. 2A is a view illustrating a specific example of an AE sourcedensity distribution.

FIG. 2B is a view illustrating an elastic wave propagation velocitydistribution.

FIG. 3A is a view illustrating a region segmentation result of an AEsource density distribution.

FIG. 3B is a view illustrating a region segmentation result of anelastic wave propagation velocity distribution.

FIG. 4 is a view illustrating an example of an evaluation resultdistribution.

FIG. 5 is a view illustrating a verification result of the validity ofthe evaluation result.

FIG. 6 is a sequence diagram illustrating a process flow of a structureevaluation system 100.

FIG. 7 is a view illustrating a basic concept of soundness evaluationusing a structure evaluation apparatus 20 according to the embodiment.

FIG. 8A is a view illustrating conventional examples of evaluatingsoundness of a structure.

FIG. 8B is a view illustrating conventional examples of evaluatingsoundness of a structure.

FIG. 9 is a view illustrating an example of an evaluation result when itis assumed that two conventional evaluation methods shown in FIGS. 8Aand 8B are combined.

FIG. 10A is a view illustrating a result of comparing AE source densitydistributions.

FIG. 10B is a view illustrating a result of comparing AE source densitydistributions.

FIG. 11 is a view illustrating another example of the basic conceptshown in FIG. 7.

FIG. 12 is a view illustrating the basic concept of the soundnessevaluation by the structure evaluation apparatus 20 in case that regionsof a predetermined ranges including the reference values are used as athresholds.

FIG. 13A is a view illustrating an evaluation method used in a case thatthe predetermined condition is that the frequency of occurrence of theelastic waves (the number of detections of the elastic waves) exceedsthe predetermined first threshold.

FIG. 13B is a view illustrating an evaluation method used in a case thatthe predetermined condition is that the propagation velocity is rapidlydropped.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a structure evaluation system, a structure evaluationapparatus, and a structure evaluation method according to an embodimentwill be described with reference to the accompanying drawings.

FIG. 1 is a view illustrating a system constitution of a structureevaluation system 100 according to an embodiment. The structureevaluation system 100 is used for evaluating the soundness of astructure. In the embodiments, the term evaluation refers to determininga degree of soundness of a structure, or a state of deterioration of thestructure, based on a standard or standards. Although a bridge isdescribed as an example of a structure in the embodiment, a structure isnot necessarily limited to a bridge. For example, a structure may be anystructure as long as an elastic wave is generated in the structure dueto occurrence or development of cracks or an external impact (e.g.,rain, artificial rain, etc.). Also, a bridge is not limited to astructure constructed over a river or a valley, and includes variousstructures provided above the ground (e.g., an elevated bridge over ahighway).

The structure evaluation system 100 includes a plurality of acousticemission (AE) sensors 10-1 to 10-n (n is an integer equal to or greaterthan 2), a signal processor 11, and a structure evaluation apparatus 20.The signal processor 11 and the structure evaluation apparatus 20 areconnected to be able to communicate via a wire or wirelessly. Further,in the description below, the AE sensors 10-1. to 10-n are referred toas an AE sensor 10 when not distinguished.

The AE sensor 10 is installed in a structure. For example, the AE sensor10 is installed on a concrete floor slab of a bridge. The AE sensor 10has a piezoelectric element, detects an elastic wave (an AE wave)generated from the structure, and converts the detected elastic waveinto a voltage signal (an AE source signal). The AE sensor 10 performsprocessing such as amplification and frequency limiting on the AE sourcesignal and outputs the processing result to the signal processor 11.Instead of the AE sensor 10, an acceleration sensor can be used. In thiscase, the acceleration sensor performs processing similar to theprocessing by the AE sensor 10 to generate a processed signal and outputthe processed signal to the signal processor 11. The thickness of aconcrete slab is at least 15 cm.

The signal processor 11 receives the AE source signal processed by theAE sensor 10 as an input. The signal processor 11 performs signalprocessing, such as noise removal and parameter extraction, deemednecessary on the input AE source signal to extract an AE feature amountincluding information on the elastic wave. The information on theelastic wave is, for example, information such as an amplitude, anenergy, a rise time, a duration, a frequency, and a zero-crossing countnumber of the AE source signal. The signal processor 11 outputsinformation based on the extracted AE feature amount to the structureevaluation apparatus 20 as an AE signal. The AE signal output from thesignal processor 11 includes information such as a sensor ID, an AEdetection time, an AE source signal amplitude, an energy, a rise time,and a frequency.

Here, the amplitude of the AE source signal is, for example, a value ofthe maximum amplitude among elastic waves. The energy is, for example, avalue obtained by time integration of squared amplitude at each timepoint. The definition of energy is not limited to the above example, andmay be, for example, one approximated by using an envelope curve of awaveform. The rise time is, for example, a time T1 until an elastic waverises above a preset predetermined value from zero. The duration is, forexample, an amount of time from the start of the rise of an elastic waveuntil the amplitude becomes smaller than a preset value. The frequencyis a frequency of an elastic wave. The zero-crossing count number is,for example, the number of times that a wave crosses a reference linepassing a zero value.

The structure evaluation apparatus 20 includes a central processing unit(CPU), a memory, an auxiliary storage device or the like connected via abus, and executes an evaluation program. By executing the evaluationprogram, the structure evaluation apparatus 20 functions as an apparatusincluding a position locator 201, a velocity calculator 202, anevaluator 203, and a display 204. Further, all or some of the functionsof the structure evaluation apparatus 20 may be realized by usinghardware such as an application specific integrated circuit (ASIC), aprogrammable logic device (PLD), a field programmable gate array (FPGA),or the like. Also, the evaluation program may be recorded in acomputer-readable recording medium. The computer-readable recordingmedium is, for example, a portable medium such as a flexible disk, amagneto-optical disk, a read-only memory (ROM), a compact disc (CD)-ROMor the like, or a storage device such as a hard disk embedded in acomputer system. Also, the evaluation program may be transmitted andreceived via an electric communication line.

The position locator 201 receives an AE signal output from the signalprocessor 11 as an input. Also, the position locator 201 pre-storesinformation on an installation position of the AE sensor 10 in thestructure thereinafter referred to as “sensor position information”) bymatching the information to a sensor ID. The information on theinstallation position is, for example, latitude and longitude, or adistance in the horizontal direction and the vertical direction from aspecific position on the structure, and the like. The position locator201 locates a position of an AE source on the basis of the informationsuch as the sensor ID and the AE detection time included in the input AEsignal and the pre-stored sensor position information. The positionlocator 201 derives (calculates) an AE source density distribution (wavesource distribution) by using the position location results for acertain period. The AE source density distribution represents thedistribution showing the wave sources of the elastic waves generated inthe structure. The position locator 201 outputs the derived AE sourcedensity distribution to the evaluator 203.

The velocity calculator 202 receives the AE signal output from thesignal processor 11 as an input. Also, the velocity calculator 202pre-stores the sensor position information by matching the sensorposition information to a sensor ID. The velocity calculator 202 derivesan elastic wave propagation velocity distribution of the structure onthe basis of the information such as the sensor IDs and the AE detectiontimes included in the input AE signals and the pre-stored sensorposition information. The elastic wave propagation velocity distributionrepresents a distribution showing the propagation velocity of theelastic waves generated in the structure. For example, the velocitycalculator 202 derives the elastic wave propagation velocitydistribution of the structure using an AE tomography analysis method.The velocity calculator 202 outputs the derived elastic wave propagationvelocity distribution to the evaluator 203. The AE tomography analysismethod is a method in which elastic waves generated from a structure aredetected by a plurality of AE sensors, a position of an AE source islocated, and propagation velocities of an analysis model of thestructure is corrected so that an error between a theoretical travelingtime and a measured traveling time from the source to each sensorconverges to within a tolerance range, to obtain the elastic wavepropagation velocity distribution in the structure. Because a velocityof AE traveling inside decreases as a structure deteriorates, the degreeof deterioration inside the structure can be evaluated from the AEvelocity distribution by using the AE tomography analysis method.

The evaluator 203 receives the AE source density distribution outputfrom the position locator 201 and the elastic wave propagation velocitydistribution output from the velocity calculator 202 as inputs. Theevaluator 203 evaluates the soundness of the structure on the basis ofthe input AE source density distribution and elastic wave propagationvelocity distribution. The evaluator 203 makes the display 204 displaythe evaluation result.

The display 204 is an image display device such as a liquid crystaldisplay or an organic electro-luminescence (EL) display. The display 204displays an evaluation result in accordance with the control of theevaluator 203. The display 204 may be an interface for connecting theimage display device to the structure evaluation apparatus 20. In thiscase, the display 204 generates an image signal for displaying theevaluation result and outputs the image signal to the image displaydevice connected thereto.

FIG. 2A shows the AE source density distribution, and FIG. 2B shows theelastic wave propagation velocity distribution. The AE source densitydistribution and the elastic wave propagation velocity distribution aredistributions obtained on the basis of the same region of the samestructure. FIGS. 2A and 2B illustrates a result of using fifteen AEsensors 10 on a floor slab of a structure of a certain road. In FIG. 2A,the horizontal axis and the vertical axis represent the length (mm) inthe horizontal direction from a specific position on the structure to beevaluated and the length (mm) in the vertical direction from thespecific position on the structure to be evaluated. Further, in FIG. 2B,the horizontal axis and the vertical axis represent the horizontallength (m) and the vertical length (m) from a specific position on thestructure to be evaluated.

In FIG. 2A, a region is shown more darkly as the number of wave sourcesbecomes larger (as the wave sources become more densely arranged), and aregion is shown more lightly as the number of wave sources becomessmaller (as the wave sources becomes more sparsely arranged). Forexample, a region 30 in FIG. 2A represents a region in which the numberof wave sources is larger than in other regions. Further, in FIG. 2B, aregion is shown more darkly as the propagation velocity becomes higher,and a region is shown more lightly as the propagation velocity becomeslower. The AE source density distribution and the elastic wavepropagation velocity distribution shown in FIGS. 2A and 2B are input tothe evaluator 203.

Hereinafter, with reference to FIGS. 3A, 3B and 4, specific processingof the evaluator 203 will be described.

On the basis of a reference value related to the density of the wavesources (hereinafter referred to as “density reference value”), theevaluator 203 segments the input AE source density distribution into tworegions, including a region in which the wave sources are sparselyarranged and a region in which the wave sources are densely arranged.Specifically, the evaluator 203 segments the AE source densitydistribution by binarizing the AE source density distribution on thebasis of the density reference value. In the embodiment, the densityreference value is set as 0.5. The evaluator 203 segments the AE sourcedensity distribution by binarizing a region having a density higher thanthe density reference value as a region in which the wave sources aredensely arranged and a region having a density lower than the densityreference value as region in which the wave sources are sparselyarranged. The density reference value is not necessarily limited to theabove value and may be appropriately changed.

Further, on the basis of a reference value related to the propagationvelocity of the elastic wave (hereinafter referred to as “propagationvelocity reference value”), the evaluator 203 segments the input elasticwave propagation velocity distribution into two regions, including aregion in which the propagation velocity is high and a region in whichthe propagation velocity is low. Specifically, the evaluator 203segments the elastic wave propagation velocity distribution bybinarizing the elastic wave propagation velocity distribution on thebasis of the propagation velocity reference value. In the embodiment,the propagation velocity reference value is set as 3800 m/s. Theevaluator 203 segments the elastic wave propagation velocitydistribution by binarizing a region having a propagation velocity higherthan the propagation velocity reference value as a region in which thepropagation velocity is high and a region having a propagation velocitylower than the propagation velocity reference value as a region is whichthe propagation velocity is low. The propagation velocity referencevalue is not necessarily limited to the above value and may beappropriately changed.

FIG. 3A shows a region segmentation result of the AE source densitydistribution, and FIG. 3B shows a region segmentation result of theelastic wave propagation velocity distribution. Hereinafter, the viewshown in FIG. 3A is described as a binarized AE source densitydistribution, and the view shown in FIG. 3B is described as a binarizedelastic wave propagation velocity distribution.

Then, the evaluator 203 evaluates the soundness of the structure usingthe binarized AE source density distribution and the binarized elasticwave propagation velocity distribution. Specifically, the evaluator 203superimposes the binarized AE source density distribution and thebinarized elastic wave propagation velocity distribution to evaluate thesoundness of the structure as four phases according to the result ofsegmentation of the superimposed region. Here, a specific example of thefour phases for evaluation may include Sound, Intermediate deteriorationI, Intermediate deterioration II and Limit deterioration. Sound,Intermediate deterioration I, Intermediate deterioration II, and Limitdeterioration represent a progress of deterioration of a structure inthat order. In other words, Sound indicates that the deterioration ofthe structure has not progressed most, and a phase approaching Limitdeterioration indicates that the deterioration of the structure hasprogressed. Based on the following evaluation conditions, the evaluator203 evaluates to which of Sound, Intermediate deterioration I,Intermediate deterioration II, and Limit deterioration each region (eachof the superimposed regions) of the structure corresponds.

(Evaluation Conditions)

Sound: “sparse” region in the binarized AE source density distributionand “high” region in the binarized elastic wave propagation velocitydistribution

Intermediate deterioration I: “dense” region in the binarized AE sourcedensity distribution and “high” region in the binarized elastic wavepropagation velocity distribution

Intermediate deterioration II: “dense” region in the binarized AE sourcedensity distribution and “low” region in the binarized elastic wavepropagation velocity distribution

Limit deterioration: “sparse” region in the binarized AE source densitydistribution and “low” region in the binarized elastic wave propagationvelocity distribution

As described above, when the superimposed region is a region in whichthe wave sources are sparsely arranged and a region in which thepropagation velocity is high, the evaluator 203 evaluates the region asa region in a Sound phase. When the superimposed region is a region inwhich the wave sources are densely arranged and a region in which thepropagation velocity is high, the evaluator 203 evaluates the region asa region in an Intermediate deterioration I phase. Further, when thesuperimposed region is a region in which the wave sources are denselyarranged and the propagation velocity is low, the evaluator 203evaluates that region as a region in an Intermediate deterioration IIphase. Further, when the superimposed region is a region in which thewave sources are sparsely arranged and the propagation velocity is low,the evaluator 203 evaluates the region as a region in a Limitdeterioration phase.

As described above, by evaluating to which of Sound, Intermediatedeterioration I, Intermediate deterioration II, and Limit deteriorationeach of the superimposed regions corresponds, the evaluator 203 derivesan evaluation result distribution in which an evaluation result of eachof the regions is shown. For example, in the evaluation resultdistribution, the evaluator 203 indicates a region in a Sound phase as“1”, a region in an Intermediate deterioration I phase as “2”, a regionin an Intermediate deterioration II phase as “3”, and a region in aLimit deterioration phase as “4.” The evaluator 203 makes the display204 display the derived evaluation result distribution.

FIG. 4 is a view illustrating an example of the evaluation resultdistribution. An operator or a manager can easily find out which regionof a structure is deteriorating with the evaluation result distributiondisplayed as illustrated in FIG. 4.

FIG. 5 is a view illustrating a verification result of the validity ofthe evaluation result. FIG. 5 shows results of collecting and checkingthe inside of a floor slab of the structure shown in FIG. 4. FIG. 5shows a core sample collected from a portion of a circle 31 in theregion “4” indicating a Limit deterioration phase in FIG. 4. Asillustrated in FIG. 5, it can be seen that deterioration inside the coresample has progressed to an extent that the core may be separated due tohorizontal cracks. On the other hand, FIG. 5 shows a core samplecollected from a portion of a circle 32 in the region “1” indicating aSound phase in FIG. 4. As illustrated in FIG. 5, cracks are not seenwith visual observation inside the core sample. Thus, the effectivenessof the evaluation method with the structure evaluation apparatus 20 isconfirmed. The length of a core sample as shown in FIG. 5 is about 23.5cm. The structure evaluation apparatus 20 can evaluate the state ofdeterioration of the structure at at least a depth of 15 cm.

FIG. 6 is a sequence diagram illustrating the process flow of thestructure evaluation system 100. In FIG. 6, each of the AE sensors 10and the signal processor 11 is a sensor unit.

Each of the AE sensors 10 detects an elastic wave (an AE wave) generatedby a structure (Step S101). The AE sensor 10 converts the detectedelastic wave into a voltage signal (an AE source signal), performsprocessing such as amplification and frequency limiting on the AE sourcesignal, and outputs the result to the signal processor 11. The signalprocessor 11 performs signal processing, such as noise removal andparameter extraction, deemed necessary on the input AE source signal(Step S102). The signal processor 11 outputs information based on an AEfeature amount extracted by performing signal processing to thestructure evaluation apparatus 20 as an AE signal (Step S103). Theprocess from Step S101 to Step S103 is executed for a predeterminedperiod.

The position locator 201 locates a position of the AE source on thebasis of the AE signal output from the signal processor 11 and thepre-stored sensor position information (Step S104). The position locator201 executes the process of Step S104 for a predetermined period. Then,the position locator 201 derives the AE source density distributionusing the position location results for the predetermined period (StepS105). The position locator 201 outputs the derived AE source densitydistribution to the evaluator 203.

Based on the AE signals output from the signal processor 11, thevelocity calculator 202 derives the elastic wave propagation velocitydistribution of the structure (Step S106). For example, the velocitycalculator 202 may derive the elastic wave propagation velocitydistribution using the AE signals for a predetermined period, or mayderive the elastic wave propagation velocity distribution using AEsignals for a period shorter than the predetermined period. The velocitycalculator 202 outputs the derived elastic wave propagation velocitydistribution to the evaluator 203. Step S105 and Step S106 may beperformed in any order.

The evaluator 203 derives the binarized AE source density distributionand the binarized elastic wave propagation velocity distribution bybinarizing each of the AE source density distribution output from theposition locator 201 and the elastic wave propagation velocitydistribution output from the velocity calculator 202 (Step S107). Usingthe derived binarized AE source density distribution and binarizedelastic wave propagation velocity distribution, the evaluator 203derives the evaluation result distribution by evaluating each region ofthe structure on the basis of the evaluation conditions (Step S108). Theevaluator 203 makes the display 204 display the derived evaluationresult distribution. The display 204 displays the evaluation resultdistribution according to control of the evaluator 203 (Step S109).

FIG. 7 is a view illustrating a basic concept of soundness evaluationusing the structure evaluation apparatus 20 according to the presentembodiment. As illustrated in FIG. 7, in the structure evaluationapparatus 20 according to the present embodiment, the high and low levelof the elastic wave propagation velocity and the degree of the AE sourcedensity each are on two-dimensional evaluation axes which are dividedinto 4 quadrants. Then, the structure evaluation apparatus 20distinguishes the four quadrants as Sound, Intermediate deterioration I,Intermediate deterioration II, and Limit deterioration on the basis ofthe evaluation conditions. Here, conventional evaluation methods arecompared with the evaluation method according to the embodiment.

FIG. 8A shows evaluation based only on AE source location, and FIG. 8Bsnows evaluation based only on the propagation velocity. As illustratedin FIG. 8A, in the evaluation based only on AE source location, theprobability that the structure has deteriorated becomes higher as AEsources become more densely arranged. Further, as illustrated in FIG.8B, in the evaluation based only on the propagation velocity, theprobability that the structure has deteriorated becomes higher as thepropagation velocity becomes lower.

FIG. 9 is a view illustrating an example of an evaluation result when itis assumed that the two conventional evaluation methods shown in FIGS.8A and 8B are combined. As illustrated in FIG. 9, when the twoconventional evaluation methods are simply combined, a linear change isexpected in which a region in which the elastic wave propagationvelocity is higher than a certain reference and the AE source densitydistribution is sparse (a region in which the wave sources are sparselyarranged) is in a Sound phase, and a region in which the elastic wavepropagation velocity is lower than the certain reference and the AEsource density distribution is dense (the wave sources are denselyarranged) has deteriorated and reached a Limit deterioration phase. Thisis not always a correct evaluation index because it has beenexperimentally confirmed that a structure in the Limit deteriorationstate may still have a sparse AE source density distribution and astructure which has deteriorated to some extent may still have anelastic wave propagation velocity that is substantially the same as thatin the Sound state. On the other hand, the basic concept of soundnessevaluation by the structure evaluation apparatus 20 according to theembodiment illustrated in FIG. 7 may be considered as a correctevaluation index, as can also be seen from the verification result ofthe validity of the evaluation result illustrated in FIG. 5.

According to the structure evaluation system 100 configured as describedabove, the soundness of a structure that generates an elastic wave canbe evaluated. Hereinafter, an effect thereof will be described indetail.

The structure evaluation apparatus 20 evaluates the soundness of thestructure on the basis of the evaluation conditions using the AE sourcedensity distribution obtained from the elastic wave detected by each ofthe plurality of AE sensors 10 and the elastic wave propagation velocitydistribution. As described above, the structure evaluation apparatus 20according to the embodiment can evaluate a deterioration level for eachregion of the structure by combining the AE source density distributionand the elastic wave propagation velocity distribution. Therefore, thesoundness of the structure generating elastic waves can be evaluated.Also, the structure evaluation apparatus 20 can evaluate with higheraccuracy by using a plurality of pieces of information instead of onepiece of information obtained from elastic waves.

Hereinafter, a modified example of the structure evaluation apparatus 20will be described.

Part or all of functional units of the structure evaluation apparatus 20may be provided in separate housings. For example, the structureevaluation apparatus 20 may include only the evaluator 203, and theposition locator 201, the velocity calculator 202, and the display 204may be provided in separate housings. In this case, the evaluator 203acquires the AE source density distribution and the elastic wavepropagation velocity distribution from another housing, and evaluatesthe soundness of the structure by using the acquired AE source densitydistribution and elastic wave propagation velocity distribution. Then,the evaluator 203 outputs the evaluation result to the display 204provided in another housing.

By the above constitution, by using an existing device for deriving theAE source density distribution and the elastic wave propagation velocitydistribution, the manufacturing cost of the structure evaluationapparatus 20 can be minimized.

The signal processor 11 may be provided in the structure evaluationapparatus 20. In this case, the signal processor 11 acquires an AEsource signal processed by the AE sensor 10 directly from the AE sensor10 or via a relay device (not illustrated).

In FIG. 1, although a single signal processor 11 is connected to theplurality of AE sensors 10-1 to 10-n, the structure evaluation system100 may include a plurality of signal processors 11 and have a pluralityof sensor units by the signal processors 11 being connected to the AEsensors 10, respectively.

Although the constitution in which the velocity calculator 202 derivesthe elastic wave propagation velocity distribution has been shown in theembodiment, the present invention is not necessarily limited thereto.For example, the velocity calculator 202 may be configured to derive avelocity in a region having a density equal to or greater than apredetermined threshold in the AE source density distribution shown inFIG. 2A or a velocity in a region having a density less than thepredetermined threshold value. In this case, the evaluator 203 evaluatesthe soundness of the structure using the AE source density distributionderived by the position locator 201 and the velocity derived by thevelocity calculator 202.

Further, the evaluator 203 may operate as an output control unit. Theoutput control unit controls an output unit such that it outputs theevaluation result. Here, the output unit includes the display 204, acommunication unit, and a printing unit. When the output unit is acommunication unit, the output control unit controls the communicationunit such that it transmits the evaluation result to another device.Further, when the output unit is a printing unit, the output controlunit controls the printing unit such that it prints the evaluationresult. The structure evaluation apparatus 20 may include some or all ofthe display 204, the communication unit, and the printing unit as theoutput unit and execute the above operations.

The position locator 201 may derive the AE source density distributionusing only the AE information generated from a wave source in which anamplitude of a first arrival wave of the AE is a predetermined thresholdor higher. For example, the position locator 201 may derive the AEsource density distribution using only AE information generated from awave source in which an amplitude of a first arrival wave of the AE is60 dB or more. This will be described in detail with reference to FIGS.10A and 10B. FIG. 10A shows an AE source density distribution derivedusing the AE information generated from a wave source in which anamplitude of a first arrival wave of AE is 53 dB or higher, and FIG. 10Bshows an AE source density distribution derived using the AE informationgenerated from a wave source in which an amplitude of a first arrivalwave of AE is 60 dB or higher. In consideration of the validityverification result of FIG. 5, more accurate evaluation can be performedby using only AE information generated from a wave source having apredetermined amplitude or higher as illustrated in FIG. 10B. Therefore,with such a constitution, it is possible to make a contribution toeffective deterioration diagnosis. Also, the first arrival wave refersto an elastic wave that reaches the AE sensor first when a certainelastic wave generation event (referred to as an event) that hasoccurred in the structure is detected by a plurality of AE sensors.

FIG. 11 is a view illustrating another example of the basic conceptshown in FIG. 7. In the example shown in FIG. 11, in addition to thedistinguishing in FIG. 7, An “Initial” phase corresponding to theinitial phase immediately after a structure is constructed or repairedis added. This represents a situation in which a large amount of wavesources are observed when a load is applied for the first time in theinitial state after a structure is constructed or manufactured. Thisdoes not indicate that deterioration of the structure startsimmediately, but indicates a response of the structure to the first loadexperienced by the structure. Then, the occurrence of AE decreases withrespect to the past load. Therefore, the Initial phase is positioned asthe preliminary phase of the Sound phase in FIG. 7, and it can be shownthat, after the Initial phase, a shift toward the Sound phase occurswith a decreasing number of wave sources. For example, the example shownin FIG. 11 is a phase to be taken into consideration when soundness isevaluated immediately after a structure is constructed or repaired.

The evaluator 203 may be configured to derive an evaluation resultdistribution showing only a region of limit deterioration, so that thedisplay 204 displays the evaluation result distribution as derived. Forexample, the evaluator 203 superimposes a binarized AE source densitydistribution and a binarized elastic wave propagation velocitydistribution. The evaluator 203 retrieves, in the superimposed region, aregion of the limit deterioration under the evaluation conditions and aregion in which the evaluation conditions are satisfied. The evaluator203 allocates a predetermined pattern such as a pattern of “4” andcolored as shown in FIG. 4 to the region satisfying the evaluationcondition in the region of limit deterioration without allocating thepredetermined pattern to other region not satisfying the evaluationcondition in the region of limit deterioration, so as to derive theevaluation result distribution showing only a region of limitdeterioration satisfying the evaluation condition in. The evaluator 203supplies the evaluation result distribution derived to the display 204so that the display 204 displays the evaluation result distribution asderived.

In the embodiments as described above, the evaluator 203 uses thebinarized AE source density distribution as two dimensional data and thebinarized elastic wave propagation velocity distribution as twodimensional data, to derive the evaluation result distribution as twodimensional data and allow the display 204 to display the evaluationresult distribution. The evaluator 203 uses the binarized AE sourcedensity distribution as three dimensioned data and the binarized elasticwave propagation velocity distribution as three dimensional data, toderive the evaluation result distribution as three dimensional data andallow the display 204 to display the evaluation result distribution asthree dimensional data. The three dimensional binarized AE sourcedensity distribution and the three dimensional binarized elastic wavepropagation velocity distribution can be obtained by extending the twodimensions to the three dimensions in the deriving process by theposition locator 201 and the velocity calculator 202.

In the embodiments described above, the evaluator 203 is configured tosegment the region of the AE source density distribution into tworegions, for example, wave source sparse region and wave source denseregion, based on a density reference value and also segment a region ofthe elastic wave propagation velocity distribution into two regions, forexample, high propagation velocity region (fast region) and lowpropagation velocity region (slow region) based on the propagationvelocity reference value. In a modification, the evaluator 203 may alsobe configured to use as thresholds a first region having a predeterminedrange including the density reference value and a second region having apredetermined range including the propagation velocity reference valueso as to segment the region of the AE source density distribution intothree regions, for example, a source-sparse region, a source-denseregion, and the other region different from the source-sparse region andthe source-dense region, and segment the region of the elastic wavepropagation velocity distribution into three regions, for example, ahigh propagation velocity region (fast region), a low propagationvelocity region (slow region), and the other region different from thehigh propagation velocity region (fast region) and the low propagationvelocity region (slow region). For example, the first region may beranged from 0.4 to 0.6. The second region may be from 3600 m/s to 4000m/s. In some cases, the first and second regions may be previously set.In other cases, the first and second regions may be set by a user.

As configured above, the evaluator 203 is configured to segment theregion of the AE source density distribution into the wave source denseregion which is higher in source-density than the maximum value of thefirst region, the wave source sparse which is lower in source-densitythan the minimum value of the first region, and the other region rangedin source-density between the maximum value and the minimum value of thefirst region. The evaluator 203 is configured to segment the region ofthe elastic wave propagation velocity distribution into the highpropagation velocity region which is higher in propagation velocity thanthe maximum value of the second region, the low propagation velocityregion which is lower in propagation velocity than the minimum value ofthe second region, and the other region ranged in propagation velocitybetween the maximum value and the minimum value of the second region.The basic concepts of the evaluation as configured above is as shown inFIG. 12.

FIG. 12 is a view illustrating the basic concept of the soundnessevaluation by the structure evaluation apparatus 20 in case that regionsof a predetermined ranges including the reference values are used as athresholds. As shown in FIG. 12, a first region 41 having apredetermined range including a reference value and a second region 42having a predetermined range including a reference value are used asthresholds, wherein it is possible to evaluate that it does not belongto any of the four evaluations. If however regions having predeterminedranges including the reference values are not used as thresholds, it ispossible to evaluate the sound region to be the limit deterioration dueto a slight variation of the value as shown in FIG. 7. In contrast,however, as described above, using the regions having the predeterminedranges including the reference values as the thresholds will reduce thepossibility of evaluating the sound region to be the limitdeterioration.

The evaluator 203 may use any one of the first region 41 and the secondregion 42 as the threshold to evaluate the state of deterioration.

In the embodiments described above, the evaluator 203 is configured tomake the evaluations in such a method as shown in FIG. 7, but notlimited to this method. The evaluator 203 may be configured to make theevaluations in such a method as mentioned below. For example, evaluator203 may be configured to make the evaluations in such a method as shownin FIG. 9 until a predetermined condition or conditions are satisfied,and then make the evaluation in such a method as shown in FIG. 7 oncethe predetermined condition or conditions are satisfied. Thepredetermined condition is that the frequency of occurrence of theelastic waves (the number of detection of the elastic waves) exceeds apredetermined first threshold, or that the propagation velocity rapidlydrops. The rapid drop of the propagation velocity is such that adifference between a propagation velocity calculated at a time t-1 bythe velocity calculator 202 and a propagation velocity calculated at atime t by the velocity calculator 202 exceeds the second threshold. Theevaluation based on the predetermined condition will be described withreference to FIGS. 13A and 13B. FIG. 12 is the view illustrating thebasic concept of the soundness evaluation by the structure evaluationapparatus 20 in case that the regions having the predetermined rangesincluding the reference values are used as the thresholds. As shown inFIG. 12, using the first region 41 having the predetermined rangeincluding the reference value and the second region 42 having thepredetermined range including the reference value as the thresholds willmake it possible to evaluate that it does not belong to any of the fourevaluations. If however regions having predetermined ranges includingthe reference values are not used as thresholds, it is possible toevaluate the sound region to be the limit deterioration due to a slightvariation of the value as shown in FIG. 7. In contrast, however, asdescribed above, using the regions having the predetermined rangesincluding the reference values as the thresholds will reduce thepossibility of evaluating the sound region to be the limitdeterioration.

FIG. 13A is a view illustrating an evaluation method used in a case thatthe predetermined condition is that the frequency of occurrence of theelastic waves (the number of detections of the elastic waves) exceedsthe predetermined first threshold. In FIG. 13A, the horizontal axisrepresents time T, the vertical axis represents the frequency ofoccurrence of the elastic waves. In FIG. 13A, the time t1 represents atime at which the frequency of occurrence of the elastic waves (thenumber of detections of the elastic waves) exceeds the predeterminedfirst threshold. As shown in FIG. 13A, the frequency of occurrence ofthe elastic waves generally increases as the deterioration of thestructure increases and exceeds the first threshold, and further thefrequency of occurrence of the elastic waves increases from the firstthreshold and then reaches a peak before the frequency of occurrence ofthe elastic waves decreases. The structure has such a property asdescribed. Thus, the evaluator 203 makes the evaluation in such a methodas shown in FIG. 9 until the frequency of occurrence of the elasticwaves reaches the first threshold, and then makes the evaluation in sucha method as shown in FIG. 7 after the frequency of occurrence of theelastic waves exceeds the first threshold. For example, the evaluator203 the evaluation in such a method as shown in FIG. 9 until the timet1, and then makes the evaluation in such a method as shown in FIG. 7after the time t1.

FIG. 13B is a view illustrating an evaluation method used in a case thatthe predetermined condition is that the propagation velocity is rapidlydropped. In FIG. 13B, the horizontal axis represents time T and the leftvertical axis represents the propagation velocity. As shown in FIG. 13B,the propagation velocity of the elastic waves generally decreases as thedeterioration of the structure increases. The structure has such aproperty as described. Thus, the evaluator 203 makes the evaluation insuch a method as shown in FIG. 9 until the propagation velocity of theelastic waves drops to the second threshold, and then makes theevaluation in such a method as shown in FIG. 7 after the propagationvelocity of the elastic waves dropped to the second threshold. Forexample, in FIG. 13B, the evaluator 203 the evaluation in such a methodas shown in FIG. 9 until the time t1, and then makes the evaluation insuch a method as shown in FIG. 7 after the time t1.

The evaluation method as shown in FIG. 7 uses the above-describedevaluation condition. The evaluation method as shown in FIG. 9 is thatthe evaluator 203 evaluates the state of deterioration to be the limitdeterioration as the propagation velocity of the elastic wave is belowthe reference value and as the AE source density distribution or wavesource density is dense, and evaluates the state of deterioration to besoundness as the propagation velocity of the elastic wave is above thereference value and as the AE source density distribution or wave sourcedensity is sparse. In each of FIGS. 7 and 9, the limit deteriorationrefers to a state of relative maximum deterioration degree. The maximumdeterioration degree in FIG. 7 is greater than the maximum deteriorationdegree in FIG. 9. As described above, the methods of evaluation areswitched under the condition for making a highly sensitive evaluation ofa change of the state of deterioration of the structure in a state thatthe deterioration of the structure has not yet progressed significantly.

According to at least one of the embodiments described above, thesoundness of a structure that generates elastic waves can be evaluatedby having the plurality of AE sensors 10 configured to detect elasticwaves generated from a structure, a position locator 201 configured toderive a wave source distribution on the basis of the elastic waves, thevelocity calculator 202 configured to derive a propagation velocitybased on the elastic waves, and the evaluator 203 configured to evaluatethe soundness of the structure on the basis of the wave sourcedistribution and the propagation velocity.

Although a few embodiments of the present invention have been describedabove, the embodiments are merely examples are not intended to limit thescope of the invention. The embodiments may be implemented in variousother forms, and various omissions, substitutions, and changes can bemade to the embodiments within the scope not departing from the gist ofthe invention. The embodiments and modifications thereof belong to theclaims below and their equivalents as well as the scope and gist of theinvention.

REFERENCE SIGNS LIST

10 (10-1 to 10-n) AE sensor

11 Signal processor

20 Structure evaluation apparatus

201 Position locator

202 Velocity calculator

203 Evaluator

204 Display

1. A structure evaluation system comprising: a plurality of sensorsconfigured to detect an elastic wave generated from a structure; aposition locator configured to derive a wave source distribution of theelastic waves generated from the structure, on the basis of the elasticwaves; a velocity calculator configured to derive a propagation velocityof the elastic wave generated from the structure, on the basis of theelastic waves; and an evaluator configured to evaluate soundness of thestructure on the basis of the wave source distribution and thepropagation velocity of the elastic waves.
 2. The structure evaluationsystem according to claim 1, wherein, on the basis of a reference valuerelated to a density of the wave sources of the elastic waves, theevaluator segments the wave source distribution into two regions,including a region in which the wave sources are sparsely arranged and aregion in which the wave sources are densely arranged, and evaluates aregion in which the wave sources are sparsely arranged and thepropagation velocity of the elastic wave is lower than a reference valuerelated to the propagation velocity of the elastic wave as a region inwhich deterioration of the structure is the most advanced.
 3. Thestructure evaluation system according to claim 1, wherein: the velocitycalculator derives a propagation velocity distribution indicating adistribution of the propagation velocity of the elastic waves byperforming tomography analysis based on the elastic waves; and theevaluator segments, on the basis of a reference value related to thepropagation velocity of the elastic waves, the propagation velocitydistribution into two regions, including a region in which thepropagation velocity is high and a region in which the propagationvelocity is low, and evaluates the region in which the wave sources aresparsely arranged and the propagation velocity is low as a region inwhich deterioration of the structure is the most advanced by using thewave source distribution and the propagation velocity distribution. 4.The structure evaluation system according to claim 1, wherein theevaluator is configured to retrieve a region which satisfies conditionsfor evaluating a state of deterioration of the structure to be limitdeterioration which represents that the deterioration is most advanced;to derive an evaluation result distribution showing regions satisfyingthe conditions; and to output the evaluation result distribution asderived.
 5. The structure evaluation system according to claim 1,wherein the evaluator evaluates each region of the structure as being inone of four phases, Sound, intermediate deterioration I, Intermediatedeterioration II, and Limit deterioration, derives an evaluation resultdistribution indicating to which phase among Sound, Intermediatedeterioration I, Intermediate deterioration II, and Limit deteriorationeach of the regions of the structures corresponds, and outputs thederived evaluation result distribution.
 6. The structure evaluationsystem according to claim 2, wherein the evaluator evaluates a region inwhich the wave sources are sparsely arranged and the propagationvelocity of the elastic wave is higher than a reference value related tothe propagation velocity of the elastic wave as a region in the Soundphase in which deterioration of the structure is least advanced.
 7. Thestructure evaluation system according to claim 1, wherein the positionlocator derives the wave source distribution in which a distribution ofthe wave sources having an amplitude equal to or larger than apredetermined value is shown, on the basis of amplitude information ofthe elastic waves detected by the sensors.
 8. The structure evaluationsystem according to claim 7, wherein the amplitude information of theelastic wave is information on an amplitude of a first arrival wave ofthe elastic wave in each event detected by the sensors.
 9. The structureevaluation system according to claim 1, wherein the elastic wave isgenerated from damage to a surface or an inside of the structure as aresult of stress applied to the structure.
 10. A structure evaluationapparatus comprising: a position locator configured to derive a wavesource distribution of elastic waves generated from a structure, on thebasis of the elastic waves; a velocity calculator configured to derive apropagation velocity of the elastic wave generated from the structure onthe basis of the elastic waves; and an evaluator configured to evaluatesoundness of the structure on the basis of the wave source distributionand the propagation velocity of the elastic waves.
 11. A structureevaluation method comprising: a position locating step of deriving awave source distribution of elastic waves generated from a structure, onthe basis of the elastic waves; a velocity calculating step of derivinga propagation velocity of the elastic wave generated from the structureon the basis of the elastic waves; and an evaluating step of evaluatingsoundness of the structure on the basis of the wave source distributionand the propagation velocity of the elastic waves.